1. Field of the Invention
The present invention relates to ink jet printers, and, more particularly, to ink jet printers including a plurality of jetting heaters and at least one substrate heater.
2. Description of the Related Art
An ink jet printer typically includes a printhead having a nozzle plate which is connected to and mounted in spaced apart relationship relative to a substrate. The nozzle plate includes a plurality of ink emitting orifices which are respectively disposed in association with a plurality of jetting heaters mounted on the substrate. When a particular jetting heater is actuated or fired, ink disposed adjacent thereto rapidly expands to form a vapor bubble. Ink is expelled through the ink emitting orifice by the bubble and is jetted onto the print medium.
During use, selective actuation of the plurality of jetting heaters within the printhead causes the operating temperature of the printhead to increase. The increased operating temperature of the printhead in turn causes the temperature of the ink disposed within the printhead to correspondingly increase. A change in the temperature of the ink results in a change of the physical properties of the ink, such as viscosity, surface tension, etc. It has been found that the drop mass and velocity of the ink droplets which are jetted onto the print medium vary with a change in the operating temperature of the ink within the printhead, thus affecting the print quality.
It is known to provide at least one substrate heater which is mounted on the substrate within the printhead for the purpose of maintaining the ink within the printhead at an approximate desired operating temperature, thereby providing a more uniform and improved print quality. The substrate heaters are typically actuated upon initial power-up of the printhead or during periods of inactivity of the printhead such that the ink within the printhead is maintained at an approximate desired temperature.
Conventional printheads employing one or more substrate heaters typically include driver circuitry for driving the substrate heaters which is separate from the driver circuitry for driving the jetting heaters. Using separate driver circuitry, the substrate heaters may be independently and selectively energized separate from the jetting heaters. However, the separate driver and interconnect circuitry associated with the substrate heaters increases the cost and complexity associated with the printer and printhead.
What is needed in the art is an ink jet printer having a printhead with both jetting heaters and substrate heaters, without the increased cost and complexity associated with using separate printer driver circuits as heretofore known.